1. Field of the Invention
The present invention relates to a package manufacturing method which includes plural boards bonded to each other, a cavity formed at an inner side of the plural boards, and penetration electrodes that electrically connect the inside of the cavity to the outside of the plural boards, a piezoelectric vibrator in which a piezoelectric vibrating reed is mounted on the penetration electrodes and disposed at an inner side of the cavity, and an oscillator, an electronic device, and a radio-controlled timepiece each having the piezoelectric vibrator.
2. Description of the Related Art
Recently, piezoelectric vibrators utilizing quartz or the like have been used in cellular phones and portable information terminals as the time source, the timing source of a control signal, a reference signal source, and the like. Although there are various piezoelectric vibrators of this type, an SMD (Surface Mount Device)-type piezoelectric vibrator is known as one example thereof. As the piezoelectric vibrator of this type, a three-layered piezoelectric vibrator in which a piezoelectric board having a piezoelectric vibrating reed formed thereon is interposed between a base board and a lid board is known. In this case, the piezoelectric vibrating reed is accommodated in a cavity (sealed space) that is formed between the base board and the lid board.
Moreover, in recent years, instead of the three-layered piezoelectric vibrator, a two-layered piezoelectric vibrator has also been developed. The piezoelectric vibrator of this type has a two-layered structure in which a base board and a lid board are directly bonded, and a piezoelectric vibrating reed is accommodated in a cavity formed between the two boards. The two-layered piezoelectric vibrator is ideally used as it is superior in achieving a thin profile compared with the three-layered structure.
As an example of such a two-layered piezoelectric vibrator, a piezoelectric vibrator in which a conductive member such as a silver paste is filled in penetration holes formed in a base board made of a glass material and baked so as to form penetration electrodes, and piezoelectric vibrating reeds (quartz crystal vibrators) are electrically connected to outer electrodes provided outside the base board is known (for example, see JP-A-2002-124845).
However, in the penetration electrodes formed of the silver paste, since an organic material such as resin in the silver paste is removed by baking and its volume decreases, there is a case where a recess portion is formed on the surfaces of the penetration electrodes, or a hole is opened on the penetration electrodes. The recess portion or hole of the penetration electrodes may decrease the air-tightness of the inside of the cavity or degrade conduction between the piezoelectric vibrating reeds and the outer electrodes.
In recent years, a method of forming penetration electrodes using metal pins made of metallic material has been developed. In this method, first, metal pins are inserted through penetration holes formed in a penetration electrode forming wafer. Then, a glass frit is filled into a gap between the metal pins and the penetration holes, and the glass frit is baked so as to integrate the penetration electrode forming wafer and the metal pins to each other. By using the metal pins as the penetration electrodes, stable conduction can be secured.
However, since binders of the organic material included in the glass frit are removed by baking, there is a case where a recess portion caused by a decrease in the volume is formed on the surface of the glass frit. Moreover, the recess portion on the glass frit may cause short-circuiting in a later step of forming an electrode film, for example.